Bromoalkylsilanes and their preparation



fective in the chlorination of methyl silanes.

Patented May 26, 1953 BROMOALKYLSILANES AND THEIR PREPARATION John L.Speier, .112,

Pittsburgh, Pa., assignor to Dow 'Gorning Corporation, Midland, Mich, acorporation ofMichigan No Drawing. Application June 8, 1950, Serial No.166,989

6 Claims. (Cl. 260-4482) methylsilan-es and to a method for producingbromomethyland bromoethylsilanes.

Heretofore, it has been found impossible to brominate methylandethylsilanes using methods conventional in chlorination procedures.Repeated attempts to brominate such silanes have failed under all usualconditions which are efand ethyl- An object of the present invention isto produce bromomethylsilanes.

Another object of the present invention is to provide a simple andefficient brorninating methyland ethylsil-anes and furt'her to providesuch a method in which all the bromine used forms bromides, thusavoiding the loss of valuable bromine in the .form of HBr.

accord with the present invention the bromomethylsilanes hereof are ofthe general formula (CH3)a(B1'CH2)SiCl3-a Where a has a value of from 1to 3 inclusive.

These bromomethylsilanes may be produced in accord with the methodher-col. 'This method comprises contacting a mixture of chlorine andbromine with a compound or the "general vfor mula Ra+lSiC13-G fluidstate, where R is selected from the group consisting of methyl and ethylradicals. By fluid state, it meant that the reaction may be conducted inliquid or vapor phase. This brominat-ion proceeds according to thefollowing equation:

In the above equation R radicals.

The chlorine and bromine may be contacted with the silane with thelatter in liquid phase at room temperature or above, preferably at atemperature below about 60 C. It has been found that, for example, (CH3)ssiCl and Bra do not react even at reflux temperature in the presence oflight. If, however, (CH3)3SiC1, Bra and C12 are contacted in accordanceherewith, reaction proceeds smoothly at room temperature.

If desired, a mixture of chlorine and bromine may be contacted with thealkylsilane. Alternatively, the bromine may be dissolved in thealkylsilane and chlorine bubbled into the mixture.

Alternatively, the chlorine and bromine may be contacted with the silanewith the latter in vapor phase. When vapor phase bromination is employedit is preferred to maintain the temperature between the boiling point atthe pressure emrepresents CR2 or Cal-I4 method for "invention areliquids.

*2 ployed of the organosilane being brominated, and that of thebrominated product. The brominated product is condensed as formed,whereby the product automatically is removed from the reaction zone.

"The bromi-nation may, if desired, be catalyzed by exposing the reactionmixture to light.

t might be expected that there would be a random distribution ofchlorine and bromine on the alkyl radicals and that 'i-lBr and Gillwould be obtained as lay-products. However, contrary to such anexpectation a selective type of reaction occurs. In this reaction thechlorine becomes selectively bonded to the hydrogen, thus formingtoy-produced hydrogen chloride. This is a distinct advantage of thepresent invention since all the bromine is used to form bromides. Thepossible yield of bromides is thus twice the expected yield.

The novel bromomethylsilanes of the present The bromomethylsilanes whichcontain hydrolyzable chlorine may be hydrolyzed and condensed to obtainthe methylbromomethylsiloxane which is useful as a lubricant and whichmay be employed to lubricate relatively moving metallic parts.

The compound (CH3)1;BICH2S1 obtained by brominating tetramethylsilanehas utility as an intermediate in the production of other organes-iliconmaterials. Thus, CHniBrGHzSi may be reacted with anhydrous potassiumacetate dissolved in glacial acetic acidto produce CH3) SiCI-IzOOCCHsAlpha-CzHsBrCzlliSiClz, obtained by brominating (Cal-I5) 2SiC12, may beused to produce a vinylsilane by dehydrobromination by conventionalmethods for dehydrohalogenation.

The following examples illustrate the method of the present application.

Example 1 119 parts by weight of trimethylchlorosilane was placed in areaction chamber and illuminated. To this silane at 25 C. there wereadded 5 parts or" bromine. Chlorine was then passed through the dark redsolution, which had resulted, until the solution became colorless. 46.5parts of bromin were then added and the flow of chlorine was continuedfor about 3 hours until the mixture was colorless.

The product was distilled and found to contain 61 parts of (CH3)3S1C1with a boiling point of 56.5 C., a trace of (CH3)2C1CH2SiC1 with aboiling point of 115 C. and 75 parts of the desired (CH3)2BrCH2SiCl.This latter product had a boiling point of 130 C., a refractive index at25 C. of 1.4630, a density of 1.375 at 25 C., and a specific refractionof 0.2002. There was also obtained about grams of high boiling productwhich decomposed on distilling at atmospheric pressure. No siliconbromide was found to have been produced.

Example 2 258 parts by weight of dimethyldichlorosilane was brominatedwith 79.5 parts of bromine using chlorine by the procedure described inExample 1. 1

Distillation of the product yielded 72 parts of CI-IsBI'CHzSiClz. Thiscompound had a boiling point of 140 to 141 C., a refractive index at C.of 1.4750, a density at 25 C. of 1.57 and a specific refraction of0.170. CHsBlzCI-ISiClz was obtained. This compound had a boiling pointof 85 to 91 C. at 25 mm. pressure and a refractive index at 25 C. of1.1585. Unreacted dimethyldichlorosilane was recovered.

Example 3 213 parts by weight of tetramethylsilane was brominated atreflux temperatures with 99 parts of bromine using chlorine by theprocedure described in Example 1 using a reflux condenser cooled withsolid CO2 and acetone.

The product was washed with water and distilled to yield 103 parts of(CH3)3BrCI-I2Si. This compound had a boiling point of 115-l16 C. at 748mm. and a refractive index of 1.442 at 25 C.

Example 4 of 0.200. The beta isomer had a boiling point of 128 C. at 95mm., a refractive index of 1.4908 at 25 C., a density of 1.45 at 25 0.,and a specific refraction of 0.200. A residue-of polybrominated materialwas also obtained.

Example 5 542 parts by weight of trimethylchlorosilane and 402 parts ofbromine were mixed, vaporized and fed into the bottom of a reactionzone. Chlorine was introduced into this mixture until the dark red colordisappeared. The temperature of the reaction chamber was maintainedbetween the boiling point of trimethylchlorosilane and the boiling pointof dimethylbromomethylchlorosilane, i. e. 57 to 130 C.

The product was distilled and found to contain 66 parts of unreacted(CH3)sSiCl, 582 parts of the desired (CH3)zBrCH2SiCl with the propertiesdescribed in Example 1. There was also obtained 244 parts of apolybrominated residue.

That which is claimed is:

1. The method which comprises contacting chlorine and bromine with acompound of the general formula Ra+1SiC13-a in fluid state, where a hasa value of from 2 to 4 inclusive and R is selected from the groupconsisting of methyl and ethyl radicals, whereby there is produced acomposition of the general formula R(BrR')SiC1:- where a has a value offrom 1 to 3 inclusive, and R is a radical selected from the groupconsisting of CH2 and C2H4 radicals.

2. The method in accord with claim 1 in which the reaction is conductedin liquid phase.

3. The method in accord with claim 2 where R represents a methyl radicaland R represents CH2.

4. The method in accord with claim 2 where R represents an ethyl radicaland R represents C2H4.

5. The method in accord with claim 1 in which the reaction is conductedin vapor phase.

6. The method in accord with claim 5 where R represents a methyl radicaland R represents CH2.

JOHN L. SPEIER, JR.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,572,402 Speier Oct. 23, 1951 OTHER REFERENCES 500., vol. 70

1. THE METHOD WHICH COMPRISES CONTACTING CHLORINE AND BROMINE WITH ACOMPOUND OF THE GENERAL FORMULA RA+1SICL3-A IN FLUID STATE, WHERE A HASA VALUE OF FROM 2 TO 4 INCLUSIVE AND R IS SELECTED FROM THE GROUPCONSISTING OF METHYL AND ETHYL RADICALS, WHEREBY THERE IS PRODUCED ACOMPOSITION OF THE GENERAL FORMULA RA(BRR'')SICL3-A WHERE A HAS A VALUEOF FROM 1 TO 3 INCLUSIVE, AND R'' IS A RADICAL SELECTED FROM THE GROUPCONSISTING OF CH2 AND C2H4 RADICALS.